Methanogenic communities and methane emissions from enrichments of Brazilian Amazonia soils under land-use change.

Amazonian forest conversion into agricultural and livestock areas is considered one of the activities that contribute most to the emission of greenhouse gases, including methane. Biogenic methane production is mainly performed by methanogenic Archaea, which underscores the importance of understanding the drivers shaping microbial communities involved in the methane cycling and changes in methane metabolism. Here, we aimed to investigate the composition and structure of bacterial and archaeal communities in tropical soils in response to land-use changes, emphasizing the methanogenic communities. We collected soil samples from primary forest, pasture, and secondary forest of the Amazonian region and used a strategy based on the enrichment of the methanogenic community with three different methanogenic substrates followed by measurements of methane emission, quantification of mcrA gene copies by qPCR, and total 16 S rRNA gene sequencing (metataxonomics). We observed variations in the structure of bacterial and archaeal communities of soils under different uses. The richness of methanogenic communities was higher in pasture than forest soils and this richness remained during the incubation period, and as a consequence, the enrichment induced earlier methane emission in pastures-derived samples. Furthermore, pastures enrichments exhibited methanogenic archaea networks more complex than primary and secondary forests. In conclusion, pastures harbor a richer and more responsive methanogenic community than forest samples, suggesting that conversion of forest areas to pasture may boost methane emission.

Mangrove soil as a source for novel xylanase and amylase as determined by cultivation-dependent and cultivation-independent methods.

Xylanase and α-amylase enzymes participate in the degradation of organic matter, acting in hemicellulose and starch mineralization, respectively, and are in high demand for industrial use. Mangroves represent a promising source for bioprospecting enzymes due to their unique characteristics, such as fluctuations in oxic/anoxic conditions and salinity. In this context, the present work aimed to bioprospect xylanases from mangrove soil using cultivation-dependent and cultivation-independent methods. Through screening from a metagenomic library, three potentially xylanolytic clones were obtained and sequenced, and reads were assembled into contigs and annotated. The contig MgrBr135 was affiliated with the Planctomycetaceae family and was one of 30 ORFs selected for subcloning that demonstrated only amylase activity. Through the cultivation method, 38 bacterial isolates with xylanolytic activity were isolated. Isolate 11 showed an enzymatic index of 10.9 using the plate assay method. Isolate 39 achieved an enzyme activity of 0.43 U/mL using the colorimetric method with 3,5-dinitrosalicylic acid. Isolate 39 produced xylanase on culture medium with salinity ranging from 1.25 to 5%. Partial 16S rRNA gene sequencing identified isolates in the Bacillus and Paenibacillus genera. The results of this study highlight the importance of mangroves as an enzyme source and show that bacterial groups can be used for starch and hemicellulose degradation.